Calculator inputs
Use the responsive form below. It shows three columns on large screens, two on smaller screens, and one on mobile.
Formula used
1) Estimate molecular weight
dsDNA uses approximately 660 g/mol per base pair. ssDNA and oligos use approximately 330 g/mol per nucleotide. In custom mode, your entered molecular weight is used directly.
2) Convert ng/µL into molarity
Molarity (M) = [Concentration (ng/µL) × 10-3 × Recovery Fraction] ÷ Molecular Weight (g/mol)
Molarity (nM) = Molarity (M) × 109
3) Convert concentration into amount
pmol/µL = nM ÷ 1000
Total pmol = pmol/µL × Sample Volume (µL)
4) Plan a dilution
C1 × V1 = C2 × V2
The calculator solves for V1, the stock volume needed, then subtracts it from the final volume to get diluent volume.
How to use this calculator
- Select the correct DNA sample type.
- Enter fragment length in bp or nt, unless using custom molecular weight.
- Enter stock concentration in ng/µL and available sample volume in µL.
- Adjust recovery if cleanup loss or handling loss matters.
- Add target nM and final dilution volume if you need a prep recipe.
- Press the calculate button to show the result above the form.
- Review nM, µM, pmol, copies per µL, and dilution guidance.
- Export the result as CSV or PDF for lab records.
Example data table
| Sample | Type | Length | Concentration | Volume | Approx. MW | Approx. Molarity |
|---|---|---|---|---|---|---|
| Insert Fragment | dsDNA | 500 bp | 25 ng/µL | 40 µL | 330,000 g/mol | 75.7576 nM |
| Sequencing Amplicon | dsDNA | 1,500 bp | 40 ng/µL | 25 µL | 990,000 g/mol | 40.4040 nM |
| Primer Mix | Oligo | 20 nt | 100 ng/µL | 100 µL | 6,600 g/mol | 15,151.5152 nM |
Frequently asked questions
1) Why do labs use nM instead of ng/µL?
nM tracks molecule count rather than mass alone. Two DNA fragments can share the same ng/µL value but contain very different numbers of molecules when lengths differ.
2) What is the dsDNA molecular weight factor?
This calculator uses an average value of 660 g/mol per base pair for double-stranded DNA. It is a common approximation for routine lab planning.
3) What factor is used for ssDNA and oligos?
Single-stranded DNA and oligos use an average of 330 g/mol per nucleotide. Exact oligo chemistry can vary, so custom molecular weight mode is available.
4) What does recovery percentage mean?
Recovery models usable material after cleanup, purification, transfer, or expected loss. A 90% recovery means only 90% of the entered concentration is treated as available.
5) Why might the target concentration be unreachable?
A dilution cannot create a concentration higher than the stock. If your target nM exceeds stock nM, you must concentrate the sample or prepare a stronger stock.
6) Are copy number results exact?
They are approximate. Copy count depends on the concentration, molecular weight estimate, and Avogadro’s number. It is useful for planning, not for strict absolute quantitation.
7) Should I enter bp or nt?
Use base pairs for double-stranded DNA. Use nucleotides for single-stranded DNA and oligos. The calculator adjusts the molecular weight factor based on sample type.
8) When should I use custom molecular weight?
Use custom mode when your vendor or software already provides an exact molecular weight. That improves accuracy for modified oligos or unusual nucleotide compositions.